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Biomedical subjects

A Krishnan

Publications and source records attributed to A Krishnan.

At least 55 records · Page 3Linked to original sources
PubMed2000

Validation of spot-testing kits to determine iodine content in salt.

Iodine deficiency disorders are a major public health problem, and salt iodization is the most widely practised intervention for their elimination. For the intervention to be successful and sustainable, it is vital to monitor the iodine content of salt regularly. Iodometric titration, the traditional method for measuring iodine content, has problems related to accessibility and cost. The newer spot-testing kits are inexpensive, require minimal training, and provide immediate results. Using data from surveys to assess the availability of iodized salt in two states in India, Madhya Pradesh and the National Capital Territory of Delhi, we tested the suitability of such a kit in field situations. Salt samples from Delhi were collected from 30 schools, chosen using the Expanded Programme on Immunization (EPI) cluster sampling technique. A single observer made the measurement for iodine content using the kit. Salt samples from Madhya Pradesh were from 30 rural and 30 urban clusters, identified by using census data and the EPI cluster sampling technique. In each cluster, salt samples were collected from 10 randomly selected households and all retailers. The 15 investigators performing the survey estimated the iodine content of salt samples in the field using the kit. All the samples were brought to the central laboratory in Delhi, where iodine content was estimated using iodometric titration as a reference method. The agreement between the kit and titration values decreased as the number of observers increased. Although sensitivity was not much affected by the increase in the number of observers (93.3% for a single observer and 93.9% for multiple observers), specificity decreased sharply (90.4% for a single observer and 40.4% for multiple observers). Due to the low specificity and resulting high numbers of false-positives for the kit when used by multiple observers ("real-life situations"), kits were likely to consistently overestimate the availability of iodized salt. This overestimation could result in complacency. Therefore, we conclude that until a valid alternative is available, the titration method should be used for monitoring the iodine content of salt at all levels, from producer to consumer, to ensure effectiveness of the programme.

Confidence Intervals↗
PubMed1999

Mutations in the rod outer segment membrane guanylate cyclase in a cone-rod dystrophy cause defects in calcium signaling.

Rod outer segment guanylate cyclase 1 (ROS-GC1) is a member of the subfamily of Ca(2+)-regulated membrane guanylate cyclases; and it is pivotal for vertebrate phototransduction. Two opposing regulatory modes control the activity of ROS-GC1. At nanomolar concentrations of Ca(2+), ROS-GC1 is activated by Ca(2+)-binding proteins named guanylate cyclase activating proteins (GCAPs). However, at micromolar concentrations of Ca(2+), ROS-GC1 is stimulated by S100beta [also named calcium-dependent (CD) GCAP]. This mode is not linked with phototransduction; instead, it is predicted to be involved in retinal synaptic activity. Two point mutations, E786D and R787C, in ROS-GC1 have been connected with cone-rod dystrophy (CORD6), with only one type of point mutation occurring in each family. The present study shows that the E786D mutation has no effect on the basal catalytic activity of ROS-GC1 and on its activation by GCAP1 and S100beta; however, the mutated cyclase becomes more activated by GCAP2. The R787C mutation has three consequences: (1) it causes major damage to the basal cyclase activity, (2) it makes the cyclase 5-fold more sensitive to activation by GCAP1; and 3) converts the cyclase into a form that is less sensitive to activation by GCAP2 and S100beta. Thus, the two CORD6-linked mutations in ROS-GC1, which occur at adjacent positions, result in vastly different biochemical phenotypes, and they are connected with very specific molecular defects in the Ca(2+) switching components of the cyclase. These defects, in turn, are proposed to have a profound effect on both the machinery of phototransduction and the retinal synapse. The study for the first time defines the biochemistry of CORD6 pathology in precise molecular terms.

Animals↗
PubMed1999

A second calcium regulator of rod outer segment membrane guanylate cyclase, ROS-GC1: neurocalcin.

ROS-GC represents a membrane guanylate cyclase subfamily whose distinctive feature is that it transduces diverse intracellularly generated Ca(2+) signals into the production of the second messenger cyclic GMP. An intriguing feature of the first subfamily member, ROS-GC1, is that it is both stimulated and inhibited by these signals. The inhibitory signals are processed by the cyclase activating proteins, GCAPs. The only known stimulatory signal is by the Ca(2+)-dependent guanylate cyclase activating protein, CD-GCAP. There are two GCAPs, 1 and 2, which link the cyclase with phototransduction, and one CD-GCAP, which is predicted to link ROS-GC1 with its retinal synaptic activity. Individual switches for these GCAPs and CD-GCAP have been respectively defined as CRM1, CRM3, and CRM2. This report defines the identity of a new ROS-GC1 regulator: neurocalcin. A surprising feature of the regulator is that it structurally is a GCAP but functionally behaves as a CD-GCAP. Recombinant neurocalcin stimulates ROS-GC1 in a dose-dependent fashion; the stimulation is Ca(2+)-dependent with an EC(50) of 20 microM; and the modulated domain resides at the C-terminal segment, between amino acids 731 and 1054. Previously, the residence of CRM2 has also been defined in this segment of the cyclase. However, the present study shows that the neurocalcin-regulated domain is distinct from CRM2. This is now designated as CRM4. Thus, the signal transduction mechanisms of neurocalcin and CD-GCAP are different, occurring through different modules of ROS-GC1. Neurocalcin signaling of ROS-GC1 is highly specific. It does not influence the activity of its second subfamily member, ROS-GC2, and of the other retinal guanylate cyclase, atrial natriuretic factor-receptor guanylate cyclase. In conclusion, the findings extend the concept of ROS-GC1's sensing diverse Ca(2+) signals, reveal the identity of its unexpected new Ca(2+) regulator, and show that the regulator acts through its specific cyclase domain. This represents an additional transduction mechanism of Ca(2+) signaling via ROS-GC1.

Animals↗
PubMed1999

Mutations in the promoter reveal a cause for the reduced expression of the human manganese superoxide dismutase gene in cancer cells.

Manganese superoxide dismutase (MnSOD) has been shown to play an important role in preventing the development of cancer. MnSOD activity is reduced in many transformed cells and tumor tissues. We previously showed that the reduced level of MnSOD activity in cancer cells was not due to a defect in the primary structure of MnSOD protein, but rather was due to defects in gene expression. To elucidate the cause for the reduced expression of human MnSOD in cancer, we investigated the nucleotide sequence in the regulatory region of the MnSOD gene in a normal human cell line and various human tumor cell lines. A DNA fragment spanning 3.4 kb 5' flanking region of the MnSOD gene isolated from a normal human genomic DNA library was used to determine the DNA sequence of MnSOD promoter. PCR primers were used for amplification of the 3.4 kb 5' flanking region of the human MnSOD gene in cancer cells. Sequence analysis identified three heterozygous mutations in the proximal region of the promoter in five human tumor cell lines. These mutations, clustered around the GC-rich region of the human MnSOD promoter, change the binding pattern of AP-2 and lead to a reduction in transcription activity using a luciferase reporter assay system. These results suggest that the reduced level of MnSOD expression in some tumor cells is, at least in part, due to a defect in the DNA sequence of the promoter region.

Base Sequence↗
PubMed1999

High-dose chemo/radiotherapy and autologous bone marrow or stem cell transplantation for poor-risk advanced-stage Hodgkin's disease during first partial or complete remission.

Complete remission rates of 70-90% can be achieved following combination chemotherapy for patients with advanced-stage Hodgkin's disease (HD). Patients who present with unfavorable poor prognostic factors, however, have a 5-year disease-free survival of only 40-50%. In an attempt to improve the prognosis of 20 patients with poor-risk advanced-stage HD, we evaluated the role of early high-dose therapy (HDT) and autologous bone marrow/stem cell transplantation (ASCT) during the first complete or partial remission (CR/PR). Patients were eligible for ASCT if they either achieved a PR (defined as > 50% regression) (six patients), or achieved a CR (14 patients) but had presented with three or more of the following unfavorable features: stage IV disease with bone marrow involvement or > or = 2 extranodal sites of involvement; bulky mass > 10 cm or bulky mediastinal mass > 1/3 of mediastina/thoracic ratio; B symptoms; and elevated serum lactate dehydrogenase (LDH) level. The study included 11 men (55%) and 9 women (45%). The median age was 37 years (range 20-57). Seventeen patients (85%) had stage IV disease; 14 (70%) had B symptoms; 13 (65%) had bulky mass > 10 cm; 14 (70%) had > or = 2 extra nodal sites involvement; and eight patients (40%) had elevated LDH levels. All patients were treated with standard four or 7-8 drug combination chemotherapy regimens until they achieved maximal response prior to ASCT with a median of six cycles (range 4-11). Six patients also received involved field radiotherapy to residual bulky mass > 5 cm or bony lesions before ASCT. The median time from diagnosis to ASCT was 8.6 months (range 5.5-18.9). Preparative regimens consisted of fractionated total body irradiation (FTBI) 1200 cGy in combination with etoposide 60 mg/kg and cyclophosphamide 100 mg/kg in all patients except one who had borderline pulmonary function and received lomustine 15 mg/kg instead of FTBI. All patients engrafted and there was no transplant-related mortality. One patient developed congestive cardiomyopathy at 4 years post-ASCT. All patients remain alive and in remission at a median follow-up of 42.8 months (range, 13.2-149.2). These preliminary results suggest that HDT and ASCT can be performed safely during first CR/PR in selected patients with advanced-stage HD who have an unfavorable prognosis. Further randomized studies comparing HDT and ASCT during first CR with conventional chemotherapy and ASCT at relapse in poor-risk advanced-stage HD should be conducted. The prognostic factors and risk groups described recently by an international prognostic study can be used to identify high-risk patients who may be candidates for more intensive therapy.

Adult↗
PubMed1999

Isolated cerebral hydatid cysts: a comparative study of two different types of presentations.

OBJECTIVES: To demonstrate the existence of two imaging patterns of cerebral hydatidosis and discuss its clinical importance. MATERIAL AND METHODS: A retrospective review of six cases of cerebral hydatidosis using various imaging techniques including CT, MRI, angiography and cystogram. RESULTS: Clinically the most common findings included papilloedema, headache and vomiting. Two of the cases reported recurrence of symptoms and were reoperated. The first 4 cases presented the classical signs of unilocular well defined cysts while the last two cases had multilocular, often polygonal cysts with perifocal edema, calcification and membrane detachment. CONCLUSION: Two radiologically and pathologically distinct subtypes of hydatidosis exist. Division into groups may assist decision over treatment protocol.

Adult↗
PubMed1998

Treatment of severe veno-occlusive disease with defibrotide: compassionate use results in response without significant toxicity in a high-risk population.

Hepatic veno-occlusive disease (VOD) is the most common of the regimen-related toxicities accompanying stem cell transplantation (SCT). Despite aggressive therapies, including the combination of tissue plasminogen activator (t-PA) and heparin, severe VOD is almost uniformly fatal. Defibrotide (DF) is a polydeoxyribonucleotide with activity in several vascular disorders and, unlike t-PA and heparin, produces no systemic anticoagulant effects. Nineteen patients who developed severe VOD after SCT were treated with DF on a compassionate-use basis. Patients had clinically established VOD and met risk criteria predicting progression and fatality. At the initiation of DF, all 19 patients had evidence of multiorgan dysfunction; median bilirubin was 22.3 mg/dL, 12 patients had renal insufficiency (5 dialysis dependent), 14 required oxygen supplementation, and encephalopathy was present in 8 patients. Beginning a median of 6 days after diagnosis of VOD, DF was administered intravenously in doses ranging from 5 to 60 mg/kg/d for a planned minimum course of 14 days. In no case was DF discontinued for attributable toxicity. No severe hemorrhage related to DF administration was observed. Resolution of VOD (bilirubin <2 mg/dL with improvement in other symptoms and signs) was seen in 8 patients (42%). Six of 8 responders survived past day +100, contrasted with the 2% predicted survival reported in comparable patients. The observed response rate, survival to day +100, and absence of significant DF treatment-associated toxicity are compelling and warrant further evaluation.

Adolescent↗
PubMed1998

Third calcium-modulated rod outer segment membrane guanylate cyclase transduction mechanism.

Ca2+-modulated rod outer segment membrane guanylate cyclase (ROS-GC1) has been cloned and reconstituted to show that it is regulated by two processes: one inhibitory, the other stimulatory. The inhibitory process is consistent with its linkage to phototransduction; the physiology of the stimulatory process is probably linked to neuronal transmission. In both regulatory processes, calcium modulation of the cyclase takes place through the calcium binding proteins; guanylate cyclase activating proteins (GCAP1 and GCAP2) in the case of the phototransduction process and calcium-dependent GCAP (CD-GCAP) in the case of the stimulatory process. The cyclase domains involved in the two processes are located at two different sites on the ROS-GC1 intracellular region. The GCAP1-modulated domain resides within the aa 447-730 segment of ROS-GC1 and the CD-GCAP-modulated domain resides within the aa 731-1054 segment. In the present study the GCAP2-dependent Ca2+ modulation of the cyclase activity has been reconstituted using recombinant forms of GCAP2 and ROS-GC1, and its mutants. The results indicate that consistent to phototransduction, GCAP2 at low Ca2+ concentration (10 nM) maximally stimulates the cyclase activity of the wild-type and its mutants: ext (deleted aa 8-408), kin (deleted aa 447-730) and hybrid consisting of the ext, transmembrane and kin domains of ANF-RGC and the C-terminal domain, aa 731-1054, of ROS-GC1. In all cases, it inhibits the cyclase activity with an IC50 of about 140 nM. A previous study has shown that under identical conditions the kin and the hybrid mutant are at best only minimally stimulated. Thus, the GCAP1 and GCAP2 signal transduction mechanisms are different, occurring through different modules of ROS-GC1. These findings also demonstrate that the intracellular region of ROS-GC1 is composed of multiple modules, each designed to mediate a particular calcium-specific signalling pathway.

Animals↗
PubMed1998

Rod outer segment membrane guanylate cyclase type 1 (ROS-GC1) gene: structure, organization and regulation by phorbol ester, a protein kinase C activator.

At present there are two recognized members of the ROS-GC subfamily of membrane guanylate cyclases. They are ROS-GC1 and ROS-GC2. A distinctive feature of this family is that its members are not switched on by the extracellular peptide hormones; instead, they are modulated by intracellular Ca2+ signals, consistent to their linkage with phototransduction. An intriguing feature of ROS-GC1, which distinguishes it from ROS-GC2, is that it has two Ca2+ switches. One switch inhibits the enzyme at micromolar concentrations of Ca2+, as in phototransduction; the other, stimulates. The stimulatory switch, most likely, is linked to retinal synaptic activity. Thus, ROS-GC1 is linked to both phototransduction and the synaptic activity. The present study describes (1) the almost complete structural identity of 18.5 kb ROS-GC1 gene; (2) its structural organization: the gene is composed of 20 exons and 19 introns with classical GT/AG boundaries; (3) the activity of the ROS-GC1 promoter assayed through luciferase reporter in COS cells; and (4) induction of the gene by phorbol ester, a protein kinase C (PKC) activator. The co-presence of PKC and ROS-GC1 in photoreceptors suggests that regulation of the ROS-GC1 gene by PKC might be a physiologically relevant phenomenon.

Animals↗
PubMed1998

Prevalence and determinants of central obesity and age-specific waist:hip ratio of people in five cities: the Indian Women's Health Study.

OBJECTIVE: To study the prevalence of central obesity and age-specific waist:hip ratio of urban women from five Indian cities. DESIGN AND SETTING: Cross-sectional surveys were conducted in 6-12 urban streets in different parts of India using similar methods of sample selection and criteria of diagnosis. SUBJECTS AND METHODS: We randomly selected 3212 women, aged 25-64 years, from Moradabad (n = 902), Trivandrum (n = 760), Calcutta (n = 365), Nagpur (n = 405), and Bombay (n = 780). Evaluation was by a questionnaire administered by a physician and a dietician, a physical examination, and anthropometric measurements. RESULTS: The overall prevalence of central obesity among the total number of women was 55.0%, with the highest prevalence in Calcutta (62.2%) and the lowest in Bombay (47.4%). Waist:hip ratio was 0.85 +/- 0.13 (mean +/- SD) with the highest ratio for women in Calcutta (0.87 +/- 0.12) and the lowest for women in Moradabad (0.84 +/- 0.16). After pooling of data from all five cities, multivariate logistic regression analysis showed that, regardless of age, body mass index (> 23 kg/m2; odds ratio 1.12), sedentary lifestyle (odds ratio 2.51), and family history of obesity (odds ratio 2.15) were strongly associated with central obesity. Excess intake of fat was weakly associated with central obesity but age was not a risk factor for central obesity, although the prevalence was highest among those aged over 55 years in Moradabad, Calcutta, and Nagpur. CONCLUSIONS: The overall prevalence of central obesity among the urban women of India has increased, more so in Calcutta and Trivandrum. Body mass index, sedentary lifestyle, and family history of excess intake of fat were significant risk factors for central obesity.

Adult↗
PubMed1995

Estrogens in unexpected places: possible implications for researchers and consumers.

Estrogenic activity originating in unexpected places was encountered on three occasions during an investigation of whether Saccharomyces cerevisiae synthesized estrogens. In each instance, estradiol found in the conditioned yeast culture medium originated from an exogenous source and was not synthesized by the yeast. In the first instance, yeast grown in the laboratory showed a time-dependent increase in estradiol in the conditioned medium. However, the culture medium supplement Bacto-peptone was found to contain large amounts of estrone. When added to yeast cultures in the form of YPD medium (yeast extract, Bacto-peptone, and dextrose), S. cerevisiae converted the estrone to estradiol leading to the accumulation of estradiol over time. In the second instance, commercially purchased S. cerevisiae grown in a molasses medium exhibited substantial amounts of estradiol. However, corn and beet molasses contained sufficient estrone and estradiol to account for the findings. As in the first instance, the yeast converted the estrone into estradiol. In the third instance, autoclaving culture medium in polycarbonate plastic flasks was found to cause an estrogenic substance to be added to the medium, whether yeast were present or not. It was determined that the autoclaving process leached bisphenol-A (BPA) out of the polycarbonate plastic. BPA was shown to bind to estrogen receptors and to induce estrogenic activity, including stimulation of MCF-7 breast cancer-cell proliferation and induction of the expression of progesterone receptors. The three instances highlight potential problems for investigators who might inadvertently add estrogens to experimental systems confounding their results. The BPA findings raise concerns about the possible addition of this estrogenic molecule to the food supply since polycarbonate plastic is used in myriad applications in the packaging of food and beverages. Although we are unaware of the substantial contamination of food products with BPA, we believe this possibility should be carefully investigated.

Benzhydryl Compounds↗
PubMed1994

Isolation, cloning, and characterization of new chitinase stored in active form in chitin-lined venom reservoir.

A 52-kDa protein was purified from the venom gland of an endoparasitic wasp Chelonus sp. near curvimaculatus. The acidic protein (pl 4.8-5.0) was purified, and the NH2-terminal amino acid sequence was determined by direct protein sequencing. A vector-anchored primer and a degenerate primer derived from an 8-amino acid region of the NH2 terminus were used in anchored polymerase chain reaction to generate a probe for screening a cDNA library prepared from mRNA from the venom gland of this wasp. A positive clone of 1596 nucleotides was isolated, sequenced, and found to contain an open reading frame encoding a protein of 483 amino acids. The amino acid sequence encoded in the cDNA clone at the amino terminus was identical to the sequence determined from the purified 52-kDa protein. Comparison of the inferred protein sequence against all of the sequences in the GenBank data base revealed a high degree of similarity to a 62-kDa insect chitinase that is expressed at each molt for the purpose of digesting the chitinous insect cuticle. Two regions that are conserved in a group of chitinases from insects, bacteria and fungi, were also conserved in the wasp 52-kDa protein. The region between amino acid residues 382 and 464 in the 52-kDa wasp chitinase markedly differed in primary sequence from the corresponding region in the 62-kDa insect chitinase, although this region in both the proteins is predicted to have a similar secondary structure predominantly of coils and turns. This region may impart unique structural properties to the 52-kDa chitinase that enables it to exist in an active form in a chitin-lined reservoir without exerting an autotoxic effect to digest the cuticular storage reservoir. Chitinolytic activity occurring in the total venom gland extract was kinetically indistinguishable from that observed for the purified 52-kDa protein, including the substrate concentrations at which maximal velocity and substrate inhibition were reached. The kinetic properties of the 52-kDa wasp chitinase were quite distinct from Serratia marcescens chitinase for both catalytic rate and substrate inhibition.

Amino Acid Sequence↗
PubMed1994

Isomeric and quaternary properties of homogenous 33 kDa protein from the venom of Chelonus near curvimaculatus.

The 33,000 Dalton venom protein of Chelonus near curvimaculatus was characterized for structural properties of charge, quaternary associations, and relationship to polydnavirus encoded proteins. Homogenous isoforms of the protein were isolated from the venom by sequential steps of 1) microdissection, 2) separation based on charge (Mono-Q column HPLC or narrow-range electrofocusing), and 3) centrifugal filtration based on molecular weight using Centricon microconcentrators. The purified protein dimerized under native conditions, and this quaternary association became denaturation resistant under certain conditions. Chemical modification of lysine epsilon amino groups did not disrupt such dimerization. The cDNA for the protein did not possess high similarity to any sequence encoded in the polydnavirus, as indicated by results of Southern blotting, but does possess similarity in its repeats to the repeats of the immunologically protective surface glycoprotein of Leishmania amazonensis.

Amino Acid Sequence↗
PubMed1993

Surfactant therapy in respiratory distress syndrome: the effect of a learning curve in improving outcome.

A retrospective study of all premature neonates who received artificial surfactant (Curosurf) at the Rotunda Hospital was performed. The period from October 1990 to June 1992 (n = 48) was compared with the initial experience from June 1987 to January 1988 (n = 15). In the initial period mortality rate was 67% in surfactant treated infants, and use of surfactant was not associated with an improvement in outcome compared with the previous six years. In the more recent period overall mortality was 21%. Overall survival in normally formed very low birthweight infants improved from 59% in 1986 to 86% in 1991-1992. Improvement in survival rates was most noticeable in infants with birthweight 750-999 grams, with survival increasing from 44% (before introduction of surfactant treatment) to 91% (in 1991-1992). It is probable that a certain level of experience with use of surfactant is required before optimal effects can be obtained.

Female↗